This invention relates to magnetic cores made from a plurality of lamination layers, such as amorphous metal, in which the edges of the lamination layers are coated with an adhesive material to support the lamination layers and to isolate the lamination layers of the magnetic core from the remainder of the transformer. More particularly, this invention relates to the application of a low-viscous thermoset resin which is allowed to cure incrementally while restraining materials are removed from the core laminations in a manner that achieves stress relief in the lamination layers without sacrificing the structural integrity of the core.
Transformer cores are commonly manufactured using silicon steel or amorphous metal. While the cores made of silicon steel are rigid and not very stress sensitive, the cores of amorphous metal, while having improved magnetic properties, are more flexible and require careful handling during manufacturing. Moreover, magnetic cores of amorphous metal are very brittle after annealing and tend to produce chips or flakes which can subsequently interfere with the normal operations of the transformer. To enhance the structural integrity of the amorphous metal cores and to increase the ease of manufacturing, amorphous metal cores are typically coated on the edges with a rigid material. In many cases, this rigid material is formed from a composite of two different materials.
At present, there are various systems used to bond the edges of the amorphous lamination layers of transformer cores. For example, one such system employs the use of a heavy solvent-based glue system. This system is employed because it can provide sufficient support to the lamination layers of the magnetic core so as to withstand the demands of the manufacturing process and yet is sufficiently flexible to allow for the release of stresses which build up in the lamination layers during the manufacturing process. However, the glue system has several disadvantages. In particular, the glue system is solvent based and thus is unfriendly from an environmental and health and safety standpoint. Moreover, the glue system provides only a minimal amount of support and is only moderately successful in preventing the penetration of amorphous flakes from the magnetic core of a transformer into the oil in which it is immersed and subsequently the coils of the transformer.
Alternatively, dual-layer, composite coatings have been employed to enhance the structural integrity and to prevent amorphous metal flake penetration. For example, U.S. Pat. No. 4,648,929 discloses the use of a dual coating of a less-rigid, inner adhesive material and a more-rigid, higher strength outer material.
Also disclosed in U.S. Pat. No. 5,441,783 is a composite material formed of a porous material which permits impregnation of a highly viscous material, i.e., a material having a viscosity of at least about 100,000 cps, and a viscous coating material having a viscosity of at least 100,000 cps.
One problem with using prior art methods for bonding the edges of amorphous metal cores is that these methods do not permit stresses in the layers of the core material to relax out. As a result, the cores contain unacceptably high losses as measured in watts.
Another problem with the prior art methods is that several production stages and sometimes a composite of different materials are required to successfully bond the edges of the amorphous metal core laminations while also preventing chip or flake penetration from the core to the coils.
Another problem with prior art methods is that it is very difficult to handle the often highly viscous materials used to bond the core laminations together. Also problematic is the chip formation that occurs during the final assembly of the laminations into a coil due to a very flexible core combined with a relatively flexible adhesive material.
The present invention relates to a magnetic core made of a plurality of lamination layers, at least a portion of which are made of amorphous metal. The lamination layers make up a core that has two edges which define opposite sides of the magnetic core. Applied to at least a portion of one side of the magnetic core is a low-stress thermoset coating material. The coating material is of sufficiently low viscosity at room temperature to permit easy application in a manufacturing environment of the coating material to the lamination layers of the magnetic core with only modest penetration of the coating material between the lamination layers. The coating material is also capable of being cured incrementally to permit stress relief within the laminations and finally curing to a rigid state of sufficient strength to hold the laminations in correct assembled relationship. The present invention also relates to a transformer made from the magnetic core described herein.